A flushing toilet system known in the prior art was configured to flush waste by means of water utilizing gravity effect only. Contrary to this, a vacuum toilet system is configured to forcedly flush waste in the toilet bowl by utilizing vacuum pressure, e.g., Patent No. JP H8-503035 A (JP 1996-503035 A). Such a system has been used mainly for transportation vehicles such as aircrafts, ships, railroad cars, etc. because of its advantage of drastically reducing volume of flushing water to be used compared to conventional gravity flushing toilet system, or of its reduced size of pipes and connecting device to be used. In the future, such vacuum flushing toilet system may be used in a wider range of areas including household usage.
In the case of a vacuum toilet system, a bowl for receiving waste is connected to a waste pipe in a substantially lower pressure condition relative to the bowl, which in turn is connected to a waste collecting tank. Generally, a small amount of water is also supplied into the bowl in conjunction with the flushing operation for cleaning the bowl. In the case of transportation means, such as an aircraft, such used waste and flushing water are disposed to a sewage treatment route after the toilet is used for a certain period of time. In order to completely flush waste in the bowl, and deliver the same effectively through the waste pipe to the waste collecting tank, a predetermined level of vacuum pressure is required in the waste pipe. Normally, such vacuum pressure level is about 40 kPa lower than atmosphere (0.3-0.5 bar of pressure difference among them). A waste water valve is connected between the exit of the bowl and the waste pipe, so as to form the above pressure difference at the valve by means of a blower or an ejector. Such pressure difference may be generated by keeping the waste collecting tank in such vacuum pressure level, or creating such vacuum pressure in conjunction with the flushing operation at the bowl. In the case of an aircraft at high altitude, pressure difference between inside and outside of the aircraft can be used. When the waste water valve is actuated by operating a flushing button, waste in the bowl is almost instantaneously flushed into the waste water pipe, and then delivered into the waste collecting tank in a high speed through the waste water pipe.
As for a problem of the vacuum toilet system, it is known that the pipe is sometimes clogged due to sucking a variety of foreign stuffs, other than the waste, which are dropped into the bowl either accidentally or intentionally. Since such problem may turn into a serious issue, especially in the case of an aircraft, some technologies for easily eliminating such obstacles are open to the public, e.g., Patent No. JP 2002-322722 A. Other solutions are also known, such as automatically closing a lid of a toilet prior to flushing the waste, and then flushing (vacuum sucking) the waste afterward, e.g., Patent No. JP 2008-546936 A. In a specific embodiment of this solution, when a user operates the flushing button, a lever located behind the lid in an open position extends and pushes the lid to a certain level of angle, so that the lid may gradually move down toward a closed position by its own weight. When a censor detects that the lid is completely closed, the censor sends a signal so as to generate vacuum pressure for flushing the waste. Through such a solution, even when the user drops some foreign stuffs accidentally, it would not drop into the bowl. Such solution can also be considered as a safety measure, such as a case when the user is a small child.